AXOLOTL. 267 



for twenty-four hours into an ample quantity of per cent, chromic-acid 

 solution ; the blastoderm is removed, washed out in water, and put for three 

 hours into Calberla's liquid (aa glycerin, water, and alcohol), and finally 

 hardened in 90 per cent, alcohol. 



The preparations are then stained with Bohn's neutral carmine ( 142) 

 for twenty-four hours (or more if of a greater thickness than 1 mm.), and 

 afterwards may, if desired, be washed out with a mixture of equal parts of 

 glycerin and water containing ^ per cent, of hydrochloric acid, which will 

 ensure a perfectly nuclear stain. Karyokinetic figures are brought out with 

 great distinctness. 



562. Sarasin's Method (SEMPEE'S Arbeiten, 1883, p. 159). Fix with 

 chromic acid or hot water, and harden with alcohol. Stain with Bismarck 

 brown, alum-carmine, or haBmatoxylin, or picro-carmine. Imbed in collodion, 

 and collodionise the sections as cut. 



Amphibia. 



563, Preliminary, In order to prepare the ova of Amphibia 

 for section cutting, it is essential to begin by removing their 

 thick coats of albumen. This may be done by putting them 

 for two or three days into 1 per cent, solution of chromic acid, 

 and shaking well ; but ova thus treated are very brittle and 

 do not afford good sections. A better method is that de- 

 scribed by WHITMAN (Amer. Natural., xxii, 1888, p. 857), and 

 by BLOCHMANN (Zool. Anz., 1889, p. 269). Whitman puts the 

 fixed eggs into a 10 per cent, solution of sodium hypochlorite 

 diluted with 5 to 6 volumes of water, and leaves them there 

 till they can be shaken free, which happens (for Necturus) in 

 a few minutes. Biochmann takes eau de Javelle (potassium 

 hypochlorite), and dilutes it with 3 to 4 volumes of water, 

 and agitates the eggs, previously fixed with solution of 

 Flemming, for fifteen to thirty minutes in it. The ova are 

 afterwards preserved in alcohol in the usual way. 



564. Axolotl. The ova are easier to prepare than those of 

 the Anura, because the yolk is separated from the albuminous 

 layer by a wide space filled with a liquid that is not coagulated 

 by reagents. Put the eggs for a few hours into picrosulphuric 

 acid, then pierce the inner chorion with fine scissors or needles, 

 and gently press out the ovum. Harden in alcohol. 



Another method that gives good results is that of 0. 

 HERTWIQ for Rana (below, 568). Stain in the mass with 

 borax-carmine, or Henneguy's acetic acid alum-carmine, and 



